ИСТИНА

The thermochemical model of mantle convection reproducing both the supercontinental and oceanic history of the Earth is formulated. The model takes into account (i) the stratification of the mantle into the upper and lower shells layers, (ii) the processes of differentiation, which lead to the formation of the light mantle material in the D"-layer, and (iii) the process of eclogitization, which is acting in the subduction zones and producing heavy material. The numerical experiments are carried out in the Boussinesq approximation with isoviscous rheology. It is found that the high degree of spherical symmetry of the young planet leads to the mantle overturn of cubic form cubic-shaped overturn of the mantle, which, in turn, determines the intensity and depth of the starting overturn. The hot initial state and rich chemical potential are expressed reflected in может быть, result in или cause active differentiation of the mantle material and formation of the bulkили most of the continental crust. It is established that, after losing its spherical symmetry and a significant part of thermochemical potential, the planet passes into megacyclic regime of evolution. Due to the dissipation или loss of heat, the upper mantle cools faster than the lower mantle; as a result, the double-layered mantle periodically если изменения не периодические в строгом смысле, то at times becomes unstable, and the mantle undergoes overturns. The time during which the upper mantle cools down или The time required for the upper mantle to cool down или The time it takes the upper mantle to cool down determines the duration of the megacycles. The configuration of the overturn, which ensures collective sinking of the cold material of the upper mantle, is energetically more favorable. Therefore, during the overturns, the global downwelling descending flows (sinks) become self-organized and assemble the supercontinents. Modeling the geodynamic evolution of the Earth, which reproduces five Wilson cycles in accordance with their geological chronology, is carried out. It is found that the positions of global sinks begin stabilizing after two Wilson cycles, and, under the action of these descending flows, the Earth acquires an asymmetrical shape. Namely, the hemisphere where the global sink is pulsating hosts the continents and the alternating Atlantic-type oceans, while the other hemisphere marked by the superplume activity is dominated by the formation of giant floor of the Pacific Ocean.